FIG. 31 is a plan view depicting a conventional ISO standard magneto-optical disk, FIG. 32 is an enlarged view of the user area thereof, FIG. 33 is a cross-sectional view thereof, and FIG. 34 is a diagram depicting the relationship between the phase pits and the MO signals thereof. As FIG. 31 shows, the magneto-optical recording medium 70 is constructed of a read-in area 71, read-out area 72 and user area 73. The read in-area 71 and the read out area 72 are ROM areas comprised of phase pits, which are formed as bumps, on a polycarbonate substrate. The depth of the phase pits in this ROM area is set such that the light intensity modulation during regeneration reaches the maximum. The area between the read-in area 71 and the read-out area 72 is the user area 73, which is a RAM area where the user can freely record information.
As the enlarged view in FIG. 32 shows, the user area 73 has the phase pits 78 to be a header area 76 and a user data area 77 in the land 75 between the grooves 74 to be the tracking guides. The user data area 77 is a flat land 75 between the grooves 74 where magneto-optical signals are recorded.
A weak laser beam is emitted to read the magneto-optical signals, then the plane of polarization of the laser beam is changed, depending on the direction of magnetization, by the polar Kerr effect, and the presence of the signals is judged by the intensity of the polarization components of the reflected light at this time. By this the RAM information can be read.
Research and development to enhance such characteristics of the magneto-optical disk memory have been ongoing, and in Japanese Patent Application Laid-Open No. H6-202820, for example, a concurrent ROM-RAM optical disk, where the simultaneous regeneration of ROM and RAM is possible, is disclosed.
Such a magneto-optical recording medium 74, where the simultaneous regeneration of ROM and RAM is possible, has a cross-sectional structure in the radius direction, as shown in FIG. 33. And the medium 74 is constructed, for example, by layering a substrate 74A, such as polycarbonate, a dielectric film 74B, a magneto-optical recording film 74C, such as TbFeCo, a dielectric film 74D, an Al film 74E and a UV (Ultra-Violet) hardened film 74F as a protective layer.
In a magneto-optical recording medium having such a structure, the ROM information is fixed-recorded by the phase pits PP of the substrate 74A, and the RAM information OMM is recorded on the phase pits PP line by magneto-optical recording, as shown in FIG. 33 and FIG. 34. The cross-section in the A-B line in the radius direction in FIG. 34 matches FIG. 33. In the example shown in FIG. 34, the phase pits PP become the tracking guides, so the grooves 74 shown in FIG. 32 are not formed.
In such a magneto-optical recording medium having ROM information and RAM information on a same recording face, many improvements exist to simultaneously regenerate the ROM information on the phase pits PP and the RAM information on the magneto-optical recording OMM.
First an obstacle to stably regenerate RAM information simultaneously with ROM information is the light intensity modulation generated in reading the ROM information, which becomes one of the causes of noise when regenerating the RAM information. For this the present applicant proposed in International Application PCT/JP02/00159 (filing date of International Application: Jan. 11, 2002) that the light intensity modulation noise is decreased by negative-feed backing the light intensity modulation signals accompany the reading of ROM information to the laser for read driving. However the noise reduction effect is insufficient with only this when the degree of the light intensity modulation of the ROM information is large.
Second the edges of the phase pits, where ROM information is recorded, disturb the polarization when RAM signals are regenerated, thereby causes noise, which is another problem.